The revolution in the use of robots in industry for many different purposes is well publicized. Articulated robot arms have been used extensively in performing many tasks including measurement and/or inspection of parts. Rotational encoders located at the joints of the articulated arm are used to determine the position of the distal end of the robot arm, which, typically carries a part to be assembled or handled. There are serious accuracy limitations on the rotational encoders available in the prior art and with the increasing demands for more and more accurate readings particularly in the assembly or inspection of finished parts, a definite need exists for improving the accuracy of the measurements provided by the encoder arrangements of existing robotic apparatus.